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+// Copyright 2018-2020 Parity Technologies (UK) Ltd.
+//
+// Licensed under the Apache License, Version 2.0 or MIT license, at your option.
+//
+// A copy of the Apache License, Version 2.0 is included in the software as
+// LICENSE-APACHE and a copy of the MIT license is included in the software
+// as LICENSE-MIT. You may also obtain a copy of the Apache License, Version 2.0
+// at https://www.apache.org/licenses/LICENSE-2.0 and a copy of the MIT license
+// at https://opensource.org/licenses/MIT.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+
+use core::{fmt, hash::{BuildHasherDefault, Hasher}, marker::PhantomData};
+
+/// A `HashMap` with an integer domain, using `NoHashHasher` to perform no hashing at all.
+///
+/// # Examples
+///
+/// See [`IsEnabled`] for use with custom types.
+///
+/// ```
+/// use nohash_hasher::IntMap;
+///
+/// let mut m: IntMap<u32, bool> = IntMap::default();
+///
+/// m.insert(0, false);
+/// m.insert(1, true);
+///
+/// assert!(m.contains_key(&0));
+/// assert!(m.contains_key(&1));
+/// ```
+#[cfg(feature = "std")]
+pub type IntMap<K, V> = std::collections::HashMap<K, V, BuildNoHashHasher<K>>;
+
+/// A `HashSet` of integers, using `NoHashHasher` to perform no hashing at all.
+///
+/// # Examples
+///
+/// See [`IsEnabled`] for use with custom types.
+///
+/// ```
+/// use nohash_hasher::IntSet;
+///
+/// let mut m = IntSet::default();
+///
+/// m.insert(0u32);
+/// m.insert(1u32);
+///
+/// assert!(m.contains(&0));
+/// assert!(m.contains(&1));
+/// ```
+#[cfg(feature = "std")]
+pub type IntSet<T> = std::collections::HashSet<T, BuildNoHashHasher<T>>;
+
+/// An alias for `BuildHasherDefault` for use with `NoHashHasher`.
+///
+/// # Examples
+///
+/// See also [`IntMap`] and [`IntSet`] for some easier usage examples.
+///
+/// ```
+/// use nohash_hasher::BuildNoHashHasher;
+/// use std::collections::HashMap;
+///
+/// let mut m: HashMap::<u8, char, BuildNoHashHasher<u8>> =
+/// HashMap::with_capacity_and_hasher(2, BuildNoHashHasher::default());
+///
+/// m.insert(0, 'a');
+/// m.insert(1, 'b');
+///
+/// assert_eq!(Some(&'a'), m.get(&0));
+/// assert_eq!(Some(&'b'), m.get(&1));
+/// ```
+pub type BuildNoHashHasher<T> = BuildHasherDefault<NoHashHasher<T>>;
+
+/// For an enabled type `T`, a `NoHashHasher<T>` implements `std::hash::Hasher` and
+/// uses the value set by one of the `write_{u8, u16, u32, u64, usize, i8, i16, i32,
+/// i64, isize}` methods as its hash output.
+///
+/// `NoHashHasher` does not implement any hashing algorithm and can only be used
+/// with types which can be mapped directly to a numeric value. Out of the box
+/// `NoHashHasher` is enabled for `u8`, `u16`, `u32`, `u64`, `usize`, `i8`, `i16`,
+/// `i32`, `i64`, and `isize`. Types that should be used with `NoHashHasher` need
+/// to implement [`IsEnabled`] and by doing so assert that their `Hash` impl invokes
+/// *only one* of the `Hasher::write_{u8, u16, u32, u64, usize, i8, i16, i32, i64,
+/// isize}` methods *exactly once*.
+///
+/// # Examples
+///
+/// See also [`BuildNoHashHasher`], [`IntMap`] and [`IntSet`] for some easier
+/// usage examples. See [`IsEnabled`] for use with custom types.
+///
+/// ```
+/// use nohash_hasher::NoHashHasher;
+/// use std::{collections::HashMap, hash::BuildHasherDefault};
+///
+/// let mut m: HashMap::<u8, char, BuildHasherDefault<NoHashHasher<u8>>> =
+/// HashMap::with_capacity_and_hasher(2, BuildHasherDefault::default());
+///
+/// m.insert(0, 'a');
+/// m.insert(1, 'b');
+///
+/// assert_eq!(Some(&'a'), m.get(&0));
+/// assert_eq!(Some(&'b'), m.get(&1));
+/// ```
+#[cfg(debug_assertions)]
+pub struct NoHashHasher<T>(u64, bool, PhantomData<T>);
+
+#[cfg(not(debug_assertions))]
+pub struct NoHashHasher<T>(u64, PhantomData<T>);
+
+impl<T> fmt::Debug for NoHashHasher<T> {
+ #[cfg(debug_assertions)]
+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ f.debug_tuple("NoHashHasher").field(&self.0).field(&self.1).finish()
+ }
+
+ #[cfg(not(debug_assertions))]
+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ f.debug_tuple("NoHashHasher").field(&self.0).finish()
+ }
+}
+
+impl<T> Default for NoHashHasher<T> {
+ #[cfg(debug_assertions)]
+ fn default() -> Self {
+ NoHashHasher(0, false, PhantomData)
+ }
+
+ #[cfg(not(debug_assertions))]
+ fn default() -> Self {
+ NoHashHasher(0, PhantomData)
+ }
+}
+
+impl<T> Clone for NoHashHasher<T> {
+ #[cfg(debug_assertions)]
+ fn clone(&self) -> Self {
+ NoHashHasher(self.0, self.1, self.2)
+ }
+
+ #[cfg(not(debug_assertions))]
+ fn clone(&self) -> Self {
+ NoHashHasher(self.0, self.1)
+ }
+}
+
+impl<T> Copy for NoHashHasher<T> {}
+
+/// Types which are safe to use with `NoHashHasher`.
+///
+/// This marker trait is an option for types to enable themselves for use
+/// with `NoHashHasher`. In order to be safe, the `Hash` impl needs to
+/// satisfy the following constraint:
+///
+/// > **One of the `Hasher::write_{u8,u16,u32,u64,usize,i8,i16,i32,i64,isize}`
+/// methods is invoked exactly once.**
+///
+/// The best way to ensure this is to write a custom `Hash` impl even when
+/// deriving `Hash` for a simple newtype of a single type which itself
+/// implements `IsEnabled` may work as well.
+///
+/// # Example
+///
+/// ```
+/// #[derive(PartialEq, Eq)]
+/// struct SomeType(u32);
+///
+/// impl std::hash::Hash for SomeType {
+/// fn hash<H: std::hash::Hasher>(&self, hasher: &mut H) {
+/// hasher.write_u32(self.0)
+/// }
+/// }
+///
+/// impl nohash_hasher::IsEnabled for SomeType {}
+///
+/// let mut m = nohash_hasher::IntMap::default();
+///
+/// m.insert(SomeType(1), 't');
+/// m.insert(SomeType(0), 'f');
+///
+/// assert_eq!(Some(&'t'), m.get(&SomeType(1)));
+/// assert_eq!(Some(&'f'), m.get(&SomeType(0)));
+/// ```
+pub trait IsEnabled {}
+
+impl IsEnabled for u8 {}
+impl IsEnabled for u16 {}
+impl IsEnabled for u32 {}
+impl IsEnabled for u64 {}
+impl IsEnabled for usize {}
+impl IsEnabled for i8 {}
+impl IsEnabled for i16 {}
+impl IsEnabled for i32 {}
+impl IsEnabled for i64 {}
+impl IsEnabled for isize {}
+
+#[cfg(not(debug_assertions))]
+impl<T: IsEnabled> Hasher for NoHashHasher<T> {
+ fn write(&mut self, _: &[u8]) {
+ panic!("Invalid use of NoHashHasher")
+ }
+
+ fn write_u8(&mut self, n: u8) { self.0 = u64::from(n) }
+ fn write_u16(&mut self, n: u16) { self.0 = u64::from(n) }
+ fn write_u32(&mut self, n: u32) { self.0 = u64::from(n) }
+ fn write_u64(&mut self, n: u64) { self.0 = n }
+ fn write_usize(&mut self, n: usize) { self.0 = n as u64 }
+
+ fn write_i8(&mut self, n: i8) { self.0 = n as u64 }
+ fn write_i16(&mut self, n: i16) { self.0 = n as u64 }
+ fn write_i32(&mut self, n: i32) { self.0 = n as u64 }
+ fn write_i64(&mut self, n: i64) { self.0 = n as u64 }
+ fn write_isize(&mut self, n: isize) { self.0 = n as u64 }
+
+ fn finish(&self) -> u64 { self.0 }
+}
+
+#[cfg(debug_assertions)]
+impl<T: IsEnabled> Hasher for NoHashHasher<T> {
+ fn write(&mut self, _: &[u8]) {
+ panic!("Invalid use of NoHashHasher")
+ }
+
+ fn write_u8(&mut self, n: u8) {
+ assert!(!self.1, "NoHashHasher: second write attempt detected.");
+ self.0 = u64::from(n);
+ self.1 = true
+ }
+
+ fn write_u16(&mut self, n: u16) {
+ assert!(!self.1, "NoHashHasher: second write attempt detected.");
+ self.0 = u64::from(n);
+ self.1 = true
+ }
+
+ fn write_u32(&mut self, n: u32) {
+ assert!(!self.1, "NoHashHasher: second write attempt detected.");
+ self.0 = u64::from(n);
+ self.1 = true
+ }
+
+ fn write_u64(&mut self, n: u64) {
+ assert!(!self.1, "NoHashHasher: second write attempt detected.");
+ self.0 = n;
+ self.1 = true
+ }
+
+ fn write_usize(&mut self, n: usize) {
+ assert!(!self.1, "NoHashHasher: second write attempt detected.");
+ self.0 = n as u64;
+ self.1 = true
+ }
+
+ fn write_i8(&mut self, n: i8) {
+ assert!(!self.1, "NoHashHasher: second write attempt detected.");
+ self.0 = n as u64;
+ self.1 = true
+ }
+
+ fn write_i16(&mut self, n: i16) {
+ assert!(!self.1, "NoHashHasher: second write attempt detected.");
+ self.0 = n as u64;
+ self.1 = true
+ }
+
+ fn write_i32(&mut self, n: i32) {
+ assert!(!self.1, "NoHashHasher: second write attempt detected.");
+ self.0 = n as u64;
+ self.1 = true
+ }
+
+ fn write_i64(&mut self, n: i64) {
+ assert!(!self.1, "NoHashHasher: second write attempt detected.");
+ self.0 = n as u64;
+ self.1 = true
+ }
+
+ fn write_isize(&mut self, n: isize) {
+ assert!(!self.1, "NoHashHasher: second write attempt detected.");
+ self.0 = n as u64;
+ self.1 = true
+ }
+
+ fn finish(&self) -> u64 {
+ self.0
+ }
+}
+
+#[cfg(test)]
+mod tests {
+ use super::*;
+
+ #[test]
+ fn ok() {
+ let mut h1 = NoHashHasher::<u8>::default();
+ h1.write_u8(42);
+ assert_eq!(42, h1.finish());
+
+ let mut h2 = NoHashHasher::<u16>::default();
+ h2.write_u16(42);
+ assert_eq!(42, h2.finish());
+
+ let mut h3 = NoHashHasher::<u32>::default();
+ h3.write_u32(42);
+ assert_eq!(42, h3.finish());
+
+ let mut h4 = NoHashHasher::<u64>::default();
+ h4.write_u64(42);
+ assert_eq!(42, h4.finish());
+
+ let mut h5 = NoHashHasher::<usize>::default();
+ h5.write_usize(42);
+ assert_eq!(42, h5.finish());
+
+ let mut h6 = NoHashHasher::<i8>::default();
+ h6.write_i8(42);
+ assert_eq!(42, h6.finish());
+
+ let mut h7 = NoHashHasher::<i16>::default();
+ h7.write_i16(42);
+ assert_eq!(42, h7.finish());
+
+ let mut h8 = NoHashHasher::<i32>::default();
+ h8.write_i32(42);
+ assert_eq!(42, h8.finish());
+
+ let mut h9 = NoHashHasher::<i64>::default();
+ h9.write_i64(42);
+ assert_eq!(42, h9.finish());
+
+ let mut h10 = NoHashHasher::<isize>::default();
+ h10.write_isize(42);
+ assert_eq!(42, h10.finish())
+ }
+
+ #[cfg(debug_assertions)]
+ #[test]
+ #[should_panic]
+ fn u8_double_usage() {
+ let mut h = NoHashHasher::<u8>::default();
+ h.write_u8(42);
+ h.write_u8(43);
+ }
+
+ #[cfg(debug_assertions)]
+ #[test]
+ #[should_panic]
+ fn u16_double_usage() {
+ let mut h = NoHashHasher::<u16>::default();
+ h.write_u16(42);
+ h.write_u16(43);
+ }
+
+ #[cfg(debug_assertions)]
+ #[test]
+ #[should_panic]
+ fn u32_double_usage() {
+ let mut h = NoHashHasher::<u32>::default();
+ h.write_u32(42);
+ h.write_u32(43);
+ }
+
+ #[cfg(debug_assertions)]
+ #[test]
+ #[should_panic]
+ fn u64_double_usage() {
+ let mut h = NoHashHasher::<u64>::default();
+ h.write_u64(42);
+ h.write_u64(43);
+ }
+
+ #[cfg(debug_assertions)]
+ #[test]
+ #[should_panic]
+ fn usize_double_usage() {
+ let mut h = NoHashHasher::<usize>::default();
+ h.write_usize(42);
+ h.write_usize(43);
+ }
+
+ #[cfg(debug_assertions)]
+ #[test]
+ #[should_panic]
+ fn i8_double_usage() {
+ let mut h = NoHashHasher::<i8>::default();
+ h.write_i8(42);
+ h.write_i8(43);
+ }
+
+ #[cfg(debug_assertions)]
+ #[test]
+ #[should_panic]
+ fn i16_double_usage() {
+ let mut h = NoHashHasher::<i16>::default();
+ h.write_i16(42);
+ h.write_i16(43);
+ }
+
+ #[cfg(debug_assertions)]
+ #[test]
+ #[should_panic]
+ fn i32_double_usage() {
+ let mut h = NoHashHasher::<i32>::default();
+ h.write_i32(42);
+ h.write_i32(43);
+ }
+
+ #[cfg(debug_assertions)]
+ #[test]
+ #[should_panic]
+ fn i64_double_usage() {
+ let mut h = NoHashHasher::<i64>::default();
+ h.write_i64(42);
+ h.write_i64(43);
+ }
+
+ #[cfg(debug_assertions)]
+ #[test]
+ #[should_panic]
+ fn isize_double_usage() {
+ let mut h = NoHashHasher::<isize>::default();
+ h.write_isize(42);
+ h.write_isize(43);
+ }
+}
+
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